Molded plastic articles, particularly injection molded plastic articles, can be made with relatively smooth surfaces by providing a relatively smooth surface for the mold in which the article is manufactured. Generally, this is accomplished by machining grinding, and lapping any portion of the mold surface which is to be replicated on a position on the plastic article where smoothness is desired. Unfortunately, it is difficult to attain a surface roughness of no more than about 12.5.times.10.sup.-8 meters (5 micro inches), RMS (root-mean-square) by such methods. Even more unfortunately, even when a desirably smooth surface is obtained it will generally have a number of voids in it and will generally later develop voids as the surface is exposed to ambient atmospheric conditions. Generally, this occurs through the oxidization or corrosion of the metal surface of the mold. Accordingly, it is difficult or impossible to obtain molded plastic articles of very high smoothness. particularly over long periods of mold operation.
Presently, certain very expensive articles, in particular the so-called rigid discs used in a number of computers, are made by depositing a memory medium such as a magnetic oxide film or forms of metallic platting on a smooth surface of a rigid aluminum disc approximately 0.187 cm thick. The preparation of the disc requires a large number of steps before it can be accepted for coating. Indeed, the surface must be polished or diamond turned to achieve a surface finish of 2.5 to 5.times.10 meters, RMS. Accordingly, it would be highly desirable to have a rigid plastic disc with sufficient surface smoothness to accept a magnetic recording medium, which disc could be mass produced at a relatively low price.
The present invention is directed to overcoming one or more of the problems as set forth above.